1. Field of the Invention
The present invention relates to an apparatus for detecting a focusing status of a taking lens, more particularly, to an apparatus for detecting a focusing status of a taking lens that determines whether the focusing status of the taking lens is front focus, rear focus, or in focus.
2. Description of the Related Art
There has been proposed an apparatus for detecting a focusing status of a taking lens that uses a plurality of image pickup devices with different optical path lengths to detect the focusing status (front focus, rear focus, or in focus) of a television lens (U.S. Pat. No. 4,333,716, and Japanese Patent Publication No. 7-60211). For example, two image pickup devices for detecting a focusing status that are intended to obtain images in the same shooting range as that of an image pickup device for obtaining an image to be outputted (image pickup device for image-output) are disposed at two places where the optical path lengths are longer and shorter than that of the image pickup device for image-output, respectively. Then, a high frequency component is extracted from the image obtained by each of the image pickup devices for detecting the focusing status, and focusing evaluation values each representing a degree of focusing onto an image pickup surface of the image pickup device for detecting the focusing status (contrast of the image) are obtained based on the respective high frequency components and compared with each other. Thus, based on the relationship of magnitudes of the focusing evaluation values, the focusing status on the image pickup surface of the image pickup device for image-output, that is, front focus, rear focus, or in focus is determined. Such the apparatus for detecting the focusing status can be applied as a focusing detecting device for automatic focusing.
Recently, a camera for a high definition (HD) system has come into use so that the number of pixels of the image pickup device for image-output has been increased compared with the conventional NTSC system. For example, while the image pickup device used in the camera for the NTSC system involves 380 thousands (768×494) of pixels, the image pickup device used in the camera for the HD system involves two millions (1920×1082) of pixels. In the case where an apparatus for detecting a focusing status is applied in the HD system, it is desired that image pickup devices according to the HD specification, that is, image pickup devices with two millions of pixels are used as the image pickup devices for detecting the focusing status as well as the image pickup device for image-output. However, the image pickup device and a peripheral circuit thereof according to the HD specification are disadvantageous in that they are more expensive, consume higher power, and include a larger circuit compared with the conventional system such as the NTSC system.